Abstract
Abstract: :
Purpose:Retinal hypoxia has been theorized to be associated with the pre–clinical stages of diabetic retinopathy. The use of a frequency–domain phosphorescence lifetime imaging (PLI) technique1 affords an opportunity to non–invasively measure retinal oxygen tension (PO2) in the diabetic retina. Using PLI, we investigated whether retinal hypoxia is present in a rat model of type I diabetes. Methods:Two–dimensional retinal oxygen tension (PO2) maps were generated in both type I diabetic rats (BBDP/Wor) and age–matched non–diabetic control rats (BBDR/Wor) using PLI. Rats were anesthetized and kept under tight physiologic control throughout the imaging process. Blood pressure, respiration rate, tidal CO2, and core body temperature were monitored and recorded continuously. Systemic blood gas was measured intermittently. PO2 maps were generated using two excitation wavelengths (λ1 = 532nm and λ2 = 412nm) and multiple modulation frequencies. The acquired phosphorescence images were processed by custom software to generate two–dimensional PO2 maps of the retinas.Results: Average PO2 in the arterial, venous, and capillary regions analyzed were, respectively, 17 ± 7 %, 11 ± 10 %, and 18 ± 13 % lower in the diabetic rats (n = 3, average age = 115 ± 8 days, duration of diabetes = 25, 29, and 48 days) when compared to controls (n = 3, average age = 130 ± 50 days). Systemic arterial PO2 was not statistically different between groups and no overt visual indications of diabetic retinopathy were present.Conclusions: While not yet statistically significant (P > 0.20), our preliminary results support the hypothesis that retinal hypoxia is present in type I diabetic rats. This suggests that PLI may allow for the pre–clinical detection of diabetic retinopathy and facilitate better treatment strategies for this devastating eye disease. 1Shonat, R.D. and A.C. Kight., Annals. Biomed. Eng. 31:1084, 2003. CR: None Support: Biomedical research grant from the Whitaker Foundation (to RDS).
Keywords: diabetic retinopathy • imaging/image analysis: non–clinical • hypoxia